One of the first things I saw Linux do was utilize two mouses with two separate mouse pointers (serial and ps2 at the time), I was a young teenager and it blew my mind and I was installing Linux at home by the end of the month.
The linux port of world of goo supported multiplayer via two mice. It was a bit of an involved setup(special udev rules if I remember correctly) but I thought it neat they took the time to make it happen.
update: I looked it up. you had to change the game config and change permissions on the mouse device. so not that bad considering.
